Polymeric blends are generally prepared by melting and mixing in mixing extruders or kneaders. The known techniques also include dissolving the polymer components together in a solvent and devolatilizing together in devolatilizing extruders.
One of the main disadvantages of many known blend systems is that, in addition to the desired improvements in the characteristics, negative influences are also discernible which are due to a more or less pronounced incompatibility of the polymer components with one another. In general, it is observed that the mechanical properties are less good than the properties theoretically to be expected (determined arithmetically).
There has been no lack of attempts hitherto to improve the compatibility of polymer blends. However, in most cases chemical modifications have been chosen for this purpose. Thus, for example, it has been attempted to improve the compatibility of polycarbonate with vinyl polymers by a free radical grafting reaction of, for example, styrene onto an unmodified polycarbonate (see British Patent Specification No. 1,245,852 and onto a polycarbonate containing allyl groups (see U.S. Pat. No. 3,692,870). An improvement in the compatibility of polycarbonate with other vinyl polymers has also been achieved by polycondensation of polycarbonate with an aliphatic vinyl polymer containing OH groups (U.S. Pat. No. 3,461,187) or with an aromatic vinyl polymer containing OH groups (see U.S. Pat. No. 3,687,895). Additives such as, for example, block polymers or graft polymers, which are compatible with both of the two polymer phases (so-called compatibility promoters) have also already been proposed for improving the compatibility of polymers which in themselves are incompatible (G. Riess, J. Kohler, C. Tournut and A. Banderet. Makromolekulare Chemie 101 (1967), pages 58-73 and L. Bohn, Kolloid Zeitschrift und Zeitschrift fur Polymere, Volume 213, Number 1-2, pages 55-67).